1. Field of Invention
The present invention relates generally to a communication system and specifically to compensation of unwanted interference and/or distortion embedded within a communications receiver.
2. Related Art
A conventional communications receiver typically includes an analog or radio frequency (RF) front end to pre-process the analog signal transmitted across the communication channel for conversion to a digital form using a suitable analog-to-digital converter (ADC). This pre-processing may include amplification, filtering, frequency conversion or mixing, gain control and other analog operations. The principal goal of this pre-processing in the conventional receiver is to minimize the dynamic range and bandwidth of the processed signal presented to the ADC which, in turn, simplifies the design of the ADC. Tradeoffs are usually made between the amount of pre-processing and the ADC complexity to minimize the cost and power dissipation of the conventional communication receiver.
Continuous advances in integrated circuit (IC) technology have often made it advantageous to allocate more of the signal processing burden to the ADC and digital circuitry. Nevertheless, conventional receiver design continues to rely on many precision RF and analog techniques. One problem common to the conventional receiver is the indirect coupling of noise and interference from other circuits in the vicinity of the receiver. These circuits may be on the same integrated circuit (IC) substrate, or may be other circuits on the printed circuit board (PCB) or elsewhere in the overall electronic system. The noise and interference may even arise from pickup of background noise such as other electronic systems sharing the same frequency spectrum. The conventional methods of compensating for the noise and interference include electromagnetic shielding, differential signal routing, and pre-amplification to boost the signal above the interference.
Another common problem is distortion in the conventional receiver. Real-world circuits cannot be made perfectly linear, and highly linear circuit designs often require high power dissipation. Distortion not only affects the fidelity of the desired signal, but also may result in distortion products of other signals and/or interference coexisting with the desired signal to appear in the desired frequency band. There are a number of problems which arise due to imperfect local oscillators or sampling clocks used in the conventional receiver. Phase noise, jitter, and spurious tones in the oscillator or clock spectra degrade the quality of the desired signal and may also fold unwanted signals into the desired frequency range.
Thus, there is a need for an apparatus and/or a method to substantially compensate for nonlinear impairments in a communication receiver that overcomes the shortcomings described above. Further aspects and advantages of the present invention will become apparent from the detailed description that follows.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.